The element cobalt is becoming increasingly important to our technical world. It is used in many applications where there are no known substitutes. The importance of cobalt to the U.S. economy has been illustrated recently by the drastic rise in the price of cobalt due to the difficulties in Zaire. With the United States importing 98% of its cobalt, we are particularly affected. The major mineral in the cobalt ore reserves of the world is cobaltite (CoAsS), occurring in many parts of the world such as in Canada, India, Australia, the U.S.S.R., Sweden, Finland, Austria, Spain, Korea, and the United States. These deposits have, for the most part, remained unexploited due to the lack of a viable metallurgical process. The U.S. deposit located in Cobalt, Idaho, is the largest known domestic reserve of cobalt. Several efforts have been made to commercially exploit cobaltite ores, without notable success. For example, in the early 1950's a small scale plant was built to recover cobalt from the Idaho deposits in which the process was based on a combined roast and flotation procedure. However, recoveries were disappointing and the process was not scaled up to full commercial operation. Subsequent attempts to use a process employing an acid-oxidizing leach under pressure were also disappointing due to severe corrosion and erosion problems which ultimately required expensive materials of construction.
Other refining and extraction processes have been researched for recovery of cobalt from cobaltic ores or concentrates, most of which have been based on a combined roast-leach procedure. See, for example, Shelton et al., U.S. Bureau of Mines R.I. 4172, January 1948 and Huttl, Engineering and Mining Journal, October 1951, pages 74-80, 121. Sill, Chemical Engineering, Jan. 13, 1958, pages 80-82, announced an alkaline ore oxidation and leach process for cobaltite which required autoclave pressures. Borvali, French Pat. No. 1,125,038, describes a leaching process with HNO.sub.3 and H.sub.2 SO.sub.4 under pressure and claims a high yield of cobalt.
Many procedures for concentrating cobaltite ores have been proposed, most of which involve a flotation procedure. See, for example, Canadian Dept. of Mines Report No. 724 and U.S. Bureau of Mines Report Nos. 4012 and 4279 as well as the Proceeding of Australian Institute of Mineral Metallurgy, No. 257, p. 37 (1976). However, such procedures have not found commercial acceptance.
Patents which disclose the recovery of cobalt from ores or concentrates include U.S. Pat. No. 2,403,640, U.S. Pat. No. 2,573,865, U.S. Pat. No. 2,694,005, U.S. Pat. No. 2,694,006, British Pat. No. 719,280, U.S. Pat. No. 2,690,391, U.S. Pat. No. 2,711,950, Canadian Pat. No. 571,320, U.S. Pat. No. 2,647,827, U.S. Pat. No. 2,647,828, U.S. Pat. No. 3,616,331, U.S. Pat. No. 3,773,891, U.S. Pat. No. 3,146,091 and U.S. Pat. No. 2,805,936. The ores of U.S. Pat. Nos. 2,647,827 and '828, 3,616,331, 3,146,091 and 3,773,891 are not an arsenic containing ore such as cobaltite. Schaufelberger U.S. Pat. No. 2,805,936 relates to cobaltite ore and appears to describe the acid-oxidizing leach process described above which requires high pressure conditions.